Many electronic communications systems require the ability to tune one or more of their circuits to selectively receive a narrow band channel within a plethora of channels in the radio spectrum. For example, a conventional radio receiver is designed to manually or automatically tune to enable reception of a selected radio signal from among many radio signals. Once the correct frequency is reached, the signal can be received down-converted to an audio signal, and presented to a user for listening. As is known, the many radio signals span a relatively wide frequency range, while each individual radio signal spans a relatively narrow frequency range, each having a different center frequency.
While the conventional radio receiver has selective tuning to tune near selected ones of the many radio signals, i.e. with selective “coarse” tuning, it should also be appreciated that the conventional radio receiver also has selective “fine” tuning, to tune within a narrower frequency range. Such fine tuning can variably move a tuned center frequency, first selected by the coarse tuning, to more accurately select a particular center frequency.
As is known, fixed electrical components suffer from component value drift with time and temperature, which can result in drift of a tuned circuit. With the selectable tuning described above, tuning drift can be overcome, and a tuning circuit, regardless of component drift, can still tune to a desired center frequency.
The radio receiver is but one example of a wide variety of electronic devices that require the ability to tune to selected frequencies. Other examples include, but are not limited to, radio transmitters, wireless telephones (voice and data), wireless modems, wireless LAN access points, analog cable modems, radar systems, and scientific instruments, and could all make use of and are based upon the design and construction and operation disclosed in earlier U.S. Pat. No. 5,964,242 of applicant Alexander H. Slocum herein.
Some characteristics that are important in determining the effectiveness of an electronic tuning circuit include a total frequency span over which the selective tuning can tune, i.e., a coarse tuning range, an accuracy of the tuning, i.e. a fine tuning range and accuracy, and a selectivity of the tuning. The selectivity will be understood to be characterized by a Q factor (or more simply “Q”), associated with a bandwidth of the tuning.
Conventional electronic circuits are known which can provide selective coarse tuning over a wide range of frequencies, but with only a relatively low Q. For example, a phase locked loop (PLL), having a programmable divider, can provide selective tuning in a relatively wide range of frequencies. Conventional electronic circuits are also known which can provide selective tuning over only a small range of frequencies, but with a high Q. For example, a varactor diode is known to provide a variable capacitance, which can be used in conjunction with a fixed inductor and other electronic components in a resonant tank circuit to provide selective fine tuning. To this end, there also exist other passive components used in tank circuits (e.g. crystals, surface acoustic wave (SAW) devices, and bulk acoustic mechanical resonators), which provide relatively high Q (on the order of a thousand), low noise, and high stability necessary for highly-selective, low-loss fine tuning at radio frequencies (RF) and intermediate frequencies (IF). While a high Q is obtained with tank circuits, if used in a radio receiver without coarse tuning circuitry, the tank circuit could not tune over the full AM and FM frequency bands. Therefore, it should be understood that with conventional circuits a tradeoff must be made between total tuning frequency range and Q.
In order to achieve both a wide range of tuning and a high Q, many conventional electronic circuits incorporate both coarse tuning circuits, which conventionally have a wide tuning range but low Q, and fine tuning circuits, which conventionally have a low tuning range but a high Q. It will, however, be understood that the coarse tuning circuits and fine tuning circuits in combination represent a relatively complex and expensive electronic structure.
To replace the circuits described above, micro electromechanical systems (GEMS) have provided on-chip voltage-tunable capacitors, low-loss inductors, and on-chip mechanical resonators. MEMS capacitors with a tuning range of approximately 3:1 at radio frequencies (RF) are known. While performance of RF MEMS capacitors and inductors have been demonstrated to be superior to those provided by conventional IC technologies, the range of achievable Q at high frequencies has been relatively low with known MEMS structures.
It would, therefore, be desirable to overcome the aforesaid and other disadvantages, and to provide an electronic circuit component capable of providing a relatively wide tuning range and a relatively high Q.